In recent years, in place of a conventional wireless system conducting a wireless communication by transmitting electromagnetic waves in a space, as shown in Patent Documents 1 and 2, a new communication system is developed and is in a practical use in which a communication is conducted by transmitting the electromagnetic field in a sheet-shaped communication medium.
As shown in FIG. 13, such a communication system has a constitution including a sheet-shaped signal transmission apparatus 1 which is a communication medium and a communication coupler 2 which is an interface.
The signal transmission apparatus 1 which is formed to have a sheet-shaped structure includes a first sheet conductive portion 3 which constitutes a lower portion electrode, a second sheet conductive portion 4 in a meshed shape arranged at a position with a gap from the first sheet conductive portion 3, a first dielectric layer 5 arranged on the second sheet conductive portion 4 and a second dielectric layer 6 arranged between the first sheet conductive portion 3 and the second sheet conductive portion 4.
Further, as shown in FIG. 13, the communication coupler 2 includes: an internal conductive body 10 in a disk shape forming a communication element; an external conductive body 12 which is formed so as to cover the internal conductive body 10 and which constitutes a coupler body 11; and a coaxial cable 13 connected to the conductive bodies 10 and 11, wherein the coaxial cable 13 is connected to a communication apparatus 14. In accordance with such a constitution, an electromagnetic field including signals input/output from the communication apparatus 14 is conducted via the coaxial cable 13 and is brought in the signal transmission apparatus 1, and after this, a communication is conducted with a second communication coupler via transmission inside the signal transmission apparatus 1.
Further, other form of the communication coupler 2 is a constitution shown in FIG. 14.
The communication coupler 15 includes: an antenna circuit 16 and a signal/electric power transmission/reception circuit (not shown in the drawings) which are in a plate shape and which are put on the signal transmission apparatus 1 for transmitting and receiving both communication signals and an electric power; and a coupler body 17 in a cup shape formed so as to cover the antenna circuit 16. In accordance with such a constitution, communication signals converted to an electromagnetic field by the antenna circuit 16 in the coupler body 17 are brought in the signal transmission apparatus 1, and after this, a communication is conducted with a second communication coupler (not shown in the drawings) via transmission inside the signal transmission apparatus 1.
In addition, similar to Patent Documents 1 and 2 as described above, techniques are disclosed in Patent Documents 3 to 5 in which an electromagnetic field is included in an area sandwiched between a pair of sheet shape bodies which are facing each other and which are electrode portions, the electromagnetic field is proceeded to conduct a communication by changing the voltage applied between a pair of the sheet shape bodies.
Specifically, a communication apparatus shown in Patent Document 1 has a signal transmission apparatus including at least one of a first signal transmission layer (second sheet conductive portion 4) and a second signal transmission layer (first sheet conductive portion 3) which is an electric power layer or a ground layer, and a switch is set between the first and second signal transmission layers by which both of them are short-ended each other.
Further, a communication apparatus shown in Patent Document 4 has a signal transmission apparatus with a laminated structure including a first conductive portion (second sheet conductive portion 4) and a second conductive portion (first sheet conductive body 3), both of which have a sheet shape (for example, form of cloth, form of paper, form of foil, form of board, form of membrane, form of film and form of mesh, and spread or extended as a surface), and a constitution is disclosed in which a loop antenna or a dipole antenna is used as a communication coupler in the signal transmission apparatus to conduct a communication.
Furthermore, a communication apparatus shown in Patent Document 5 has a signal transmission apparatus including a first conductive portion (second sheet conductive portion 4) and a second conductive portion which have a sheet shape and which are laminated, and a radio absorptive body in a wedge shape is formed on a substrate constituted from the first and second conductive bodies to avoid reflection and leakage by reducing the electromagnetic waves irradiated from communication elements.